This is the first project we have cut asphalt to allow construction stormwater to infiltrate. The area is paved, flat. The sweeper runs constantly but the water is still too turbid to go down the drain. The fill soil under the asphalt is sandy. If we just covered the catch basin with 30 Mil PVC, the area would just flood, then drain to another catch basin. Solution? Cut out a section of asphalt full depth to the sandy soil, fill with 3 to 5 inch rock. This way the water infiltrates but vehicles can drive over the hole. This is working really well so we will be doing this on future container dock upgrade projects.
The contractor had to connect a new storm system from up the hill into an existing catch basin in the foreground. After they completed the connection but before paving, they covered the pipe run with plastic and sand bags to protect from dirty water entering the catch basin. Work was completed during dry summer weather. Paving took place a couple of months later.
I can’t get away from it. It doesn’t matter where I go, I always see some type of construction erosion issue. I went to visit relatives in Portland, Maine, flying in and out of Boston Logan International. In the terminal, waiting for my flight back home, I saw a construction project on the ramp; it had rained a few says before, hard. Obviously, the stockpile had not been covered before the storm and sediment washed off the pile into the drain.
I work at an airport that operates under strict turbidity
effluent limits; here is how we do this kind of work:
(1) rarely do we allow stockpiles on the ramp because we rarely
reuse the excavated material (it is either contaminated, unsuitable or doesn’t
meet current FAA requirements); it is direct loaded into trucks and hauled off.
When we do stockpile, we place dirt on plastic and cover it with plastic, using
lots of sand bags to secure it from jet blast and wind.
(2) work areas are always isolated so there is no runoff from
the site. Normally, we use four-inch extruded asphalt curbing along the base of
the jersey barriers. Rolled hot mix asphalt (HMA) is used at the entrance point
so water is contained but vehicles can access the site. Water that builds up inside the curbing is
pumped back into the excavation if clean, or a tank if contaminated.
I should have
mentioned that we also have strict sediment trackout requirements: no visible
sediment leaves the site at any time.
This is both because of the effluent limits and for safety reasons; dirt
and debris that gets sucked up into a jet engine is damaging and possibly
deadly.
Lastly, I am
not casting aspersions on the folks at Logan; I don’t know their situation,
permits, drainage system, or tolerance for risk. Because of my situation, I have low risk tolerance
for potential non-compliance with our permit and I notice when something would
cause me grief at my airport.
When inspecting plastic cover, make sure sheets are overlapped and secured from blowing wind. Also, collect the clean runoff and direct it away from bare soil so it doesn’t get dirty.
